<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<canvas id="board" width="400px" height="300px"  style="top:100px; left: 100px; align-self: center; position: absolute;"></canvas>
		<button id="back">撤销</button>
	</body>
	<script type="text/javascript" src="final.js" ></script>
	<script>
		var test=Autograph(document.getElementById('board'));
		document.getElementById('back').addEventListener('click',test.revoke);
	</script>
</html>
